10 - Mythconceptions of the Younger Dryas
Catastrophists are demonstrably mythtaken
The previous posts demonstrated the great difficulties in reconstructing the events of the last ice age from archeological data: the sparse and often contradictory data are only rarely conclusive. Fortunately, almost continuous records of physical ice-age data exist in ice and sediment cores, which can be used as proxies for historical temperature, climate, geomagnetic field strength, solar radiation and cosmic radiation. Unfortunately, it often takes a polymath proficient in geology, climatology, biology, chemistry, astronomy, and (astro)physics to weave all the evidence strands into a self-consistent theory.
There currently is no mainstream, consensus narrative as to what caused the last glacial period to start or end. Many entertainers see this as a green light to fabricate some highly-speculative low-probability stories involving mythical catastrophes. The next 20-odd posts will demonstrate that fairly boring, high-probability “uniformitarian catastrophes” very likely caused the start and end of our last glacial period. Uniformitarian catastrophes are hereby defined as more energetic versions of historically-recorded events, for example supervolcanoes, powerful solar flares, geomagnetic excursions and failed reversals, etc. As a warmup, this post starts by debunking some of the myths surrounding the Younger Dryas (12,850 - 11,700 years BP), a period during which the processes terminating the glacial period appeared to falter, and a return to a new glacial maximum seemed likely.
Myth 1: The ice age ended with the Younger Dryas
This one is fairly easy to disprove. Our current interglacial period, the Holocene, starts at the end of the YD, so the defined end of the glacial period is the YD. However, a graph of the global sea-level rise versus age shows that the glacial melt was only halfway complete by then : sea-level had only risen by half of its eventual 120 m from the Last Glacial Maximum low. This sea level rise is almost entirely due to glacial melt waters reaching the World’s oceans. The global sea level rose an additional 60 m between 11,700 – 7000 BP, indicating that it took an additional 4700 years for the remaining half of the Eurasian and North American ice sheets to melt. Before 11,000 BP the melting occurred with starts and stops that caused pulses in the global sea level rise during the Bølling–Allerød (BA) and YD. After 11,000 BP the ice melt entered a fairly steady-state melt regime.
Myth 2: The Younger Dryas was a period of global cooling and a global return to glacial conditions
This myth you can still find on Wikipedia, but is also easily disproven. The figure above demonstrates that temperatures generally cooled in the Northern Hemisphere and warmed in the Southern Hemisphere[5]. Antarctic ice core temperature reconstructions show a ~5 °C increase (below) during the YD, indicating any return to glacial conditions during the YD was regional, not global in nature. The Global Mean Surface Temperature dropped by a (relatively minor) 0.6 °C [5].
Global sea levels rose roughly 20 m during the YD (see graph Myth 1). This rise was almost entirely due to glacial meltwaters reaching Earth’s oceans. The return to lower temperatures and a colder climate in Eurasia caused ice sheets to re-advance[1], so the bulk of the melt waters must have come from the Laurentide and Cordilleran ice sheets in North America.
Paleogeographic reconstructions of the North American ice sheet (above) show significant melting in the western and mid-western parts of Canada [2,3], causing the almost complete collapse of the Cordilleran (Northwest American) ice sheet by the end of the YD. Great Lakes reconstructions (below) demonstrate that the (Northeast American) Laurentide ice-sheet retreated to the north [4] during the YD, and that the climate in the eastern Great Lakes during the YD was anti-phased to the stereotypically warmer BA and colder YD in the rest of North America[10]. These glacial retreats disprove a return to glacial conditions in mid-western North America during the YD.
Myth 3: Megafloods caused catastrophic sea level rises before or during the YD
This is one of the more speculative ideas proposed in Hancock’s Ancient Apocalypse Netflix series (Ep. 8). Catastrophic sea level rises of more than 20 m could not have occurred during the last 20,000 years as such cataclysmic events would have decimated the World’s coral colonies. Corals live in symbiosis with Zooxanthellae, photosynthetic organisms that need sunlight to survive, so a sudden deepening of more than 20 m would have killed off large amounts of Zooxanthellae and their coral hosts, leading to a coral mega-extinction, which is not in evidence.
The global sea level rose (see graph Myth 1) in pulses during the BA and YD. For example, the sea level rose between 16-25 m over 800 years during BA “Meltwater Pulse 1A” (14,700 - 13,900 BP). Could this pulse have been caused by a single North American megaflood?
Lake Bonneville was a Late Pleistocene paleolake that covered a large area in the western US, including the area now covered by the Great Salt Lake. Around 14,500 BP the lake catastrophically burst through its banks, whereby roughly 5000 km3 of water flooded into the Pacific Ocean via the Snake River[6]. The World’s oceans currently cover ~70% of Earth’s ~500 106 km2 surface, or an area of ~350 106 km2, although in the Late Pleistocene they covered an area that was roughly 20 106 km2 smaller. Assuming a World Ocean surface area of 300 106 km2 (we’re going for order of magnitude, not accuracy) then the 5000 km3 Lake Bonneville catastrophic flood raised global sea levels by about 1.7 10-5 km = 1.7 cm. Which is significant, but hardly catastrophic. An imaginary supermegaflood from a 1 km deep lake covering all of Montana (area = 0.38 106 km2) would cause a 1.3 m sea level rise, so 15 imaginary and contemporaneous supermegafloods would be required to instantly raise global sea level by 20 m.
Myth 4: An extinction level asteroid strike caused a sudden ice melt and a sea-level surge
A 20 m rise in sea level would require roughly 300. 106 km2 * 2. 10-2 km = 6. 106 km3 of water, which is equal to 6. 1015 m3 of water, which roughly equals 6. 1018 kg and 6. 1021 g of water. If all this water was coming from glacial melting, then 6. 1021 g of ice would have to be melted. It takes 334 J to melt 1 g of ice, so this would require – at a minimum - 6. 1021 g * 334 J/g = ~2. 1024 Joules. The Chicxulub meteorite[7] – the second largest meteorite ever to hit Earth and the one likely responsible for the Cretaceous dinosaur extinction – imparted a kinetic energy of 3. 1023 J to the Earth, so a quick 20 m sea level rise would require 7 contemporaneous extinction level meteorite impacts. There is no evidence that a single large meteorite impacted the Earth at the end of the last ice age, and even if one did, it by itself could only raise sea levels by ~3 m. This 3 m rise is a maximum, as most of the meteorite’s energy would not go towards melting ice, but would be dissipated in:
the impact crater, causing rock fracturing, dispersion and melt
the heating and evaporating of ice into warm water and steam
the heating of the atmosphere.
While certainly an unpleasant surprise, a sudden 3 m sea level rise would not have wiped-out any advanced civilizations (Atlantis is mentioned by Hancock). Most ancient coastal cities, such as Rome and Athens, had their harbors at sea level (Ostia, Piraeus) but had their main buildings built inland and high above sea level: the Acropolis is 127 m above sea level, the Colosseum is 20 m above sea level and 30 km inland. The ancient city builders realized that building too close to the sea runs the risk of severe storm surges obliterating your city. This is what happened during Hurricane Katrina (8+ m storm surge) that flooded and destroyed many low elevation New Orleans parishes. Similarly, a tsunami caused by a large earthquake has much greater potential to cause severe damage: the 14 m tsunami caused by the April 1, 1946, the 8.6 Mw Aleutian Islands earthquake devastated the Hawaiian island of Hilo. Any advanced YD civilization would have certainly been prepared for an abrupt 3 m sea level rise, especially as global sea levels had already gradually risen by 30 m during the preceding BA period.
Myth 5: Comet fragment airbursts caused huge ice melts
No large impact craters dating back to the end of the last ice age have been found. Some catastrophists[e.g. 11] therefore propose that a fragmenting comet caused airbursts, whose fireballs melted significant amounts of ice. The largest recorded air burst – the Tunguska event - caused a 12 megaton (14 TW.h) explosion, but even larger, speculative 30 megaton airbursts (35 TW.h) have been contemplated[11]. Suppose a huge comet fragmented into a 10,000 pieces, each of 30 megaton size. 1 W.h equals 3.6 103 J, so 104 comet fragments deliver an energy of 35 104 TWh = 35 1016 Wh = 1.3 1021 J, which is sufficient to melt 1.3 1021 J / 334 J/g = 3.8 10 18 g of ice = 3.8 1015 kg of ice = ~4 1012 m3 of ice = 4000 km3 of ice. Assuming the ice sheets were locally 1 km thick, then together the 10,000 comet fragments could not even melt a 65 x 65 km patch of ice - roughly Greater Chicago - and would only raise sea-levels by 1.4 cm. While such airbursts would be locally catastrophic, they would fail to put even a small dent in the melting ice sheets or cause a significant sea-level rise.
Myth 6: Solar Flares / Solar Proton emissions (SPE’s) caused huge ice melts
The largest recorded solar flare was the 1859 Carrington event, whose Earth incidence caused an estimated 6 TW of Joule heating over a roughly 48 hour period, so roughly 300 TW.h or 20 times the energy of the Tunguska event. Previous events, such as the “Miyake event” that occurred roughly 14,000 years ago, were reportedly ~100 (80-160) times larger. Its energy would therefore be 3 .102 TWh * 100 magnitude scale = 3. 104 TWh.= 3. 1016 Wh = ~1020 J, which is sufficient to melt ~3. 1017 g of ice = 3. 1014 kg of ice = ~3.6 1011 m3 of ice = 360 km3 of ice. So despite a huge scale-up in size, an enormous solar flare and SPE would only be able to melt a ~20 km by ~20 km patch of a 1 km thick ice sheet, i.e. clear downtown Chicago. And even then only if its full power was focused on the ice sheet and all its power was used to just melt ice. Note that the sun emitted huge amounts of energy during the Carrington event: its flare was on the order of 4 1025 J and its Coronal Mass Ejection 3 1025 J [8], which in combination is more than enough to melt all the ice sheets a few times over. Only part of this energy hit Earth, and Earth’s surface was largely shielded from much of its incident energy by our geomagnetic field, as well as most material’s inability (e.g. ice) to interact with the magnetic pulse caused by Carrington event.
The fabled solution: the tortoise and the hare
These mythical catastrophes by themselves are demonstrably not powerful enough to melt large volumes of ice: a single, short, violent burst of energy is insufficient to cause significant melting. In addition, once the short & violent - yet minor - melting has occurred, the Earth’s climate will take over again and re-grow the ice sheets. What’s therefore required is a strong and steady power source that consistently melts the ice over long periods of time. Solar radiation energy is therefore the gorilla in the room: the bulk of the melting power must have been supplied by the 170 103 TW [9] Earth-incident solar radiation energy. In a single day, solar irradiation imparts more energy (4 106 TW.h) than the combined 5&6 catastrophes. This huge amount of energy achieves a colossal yet often under-appreciated task: it heats Earth’s surface temperature to a comfy average of 15 °C. Future posts will demonstrate that the ~ 4 TW of geothermal heat flux - Earth’s internal heat - also played an important role in melting the ice.
This is of course a bitter blow to catastrophists and thrill-seekers alike who were hoping for something a tad more juicy. What caused the ice sheets to melt? The sun? Boring! It’s like reading a complex whodunnit full of dramatic plot twists only to find out the butler did it. Fortunately, future posts will be spiced up with some truly nasty catastrophes that have sown Death! and Mayhem!. These uniformitarian catastrophes demonstrably nudged, then pushed, Earth’s climate out of its steady-state ice age. First up: what nudged the Earth out of its Last Glacial Maximum? Spoiler alert: it wasn’t a comet.
References:
[1] Andersen, B., Borns, H., 1994, The Ice Age World: An Introduction to Quaternary History and Research with Emphasis on North America and Northern Europe During the Last 2.5 Million Years. Oxford University Press, ISBN: 978-8200218104
[2] Dyke, A., 2004, An outline of North American deglaciation with emphasis on central and northern Canada, Developments in Quaternary Sciences, v2, p. 373-424, doi: https://doi.org/10.1016/S1571-0866(04)80209-4.
[3] CSDMS, 2023, Laurentide Ice Sheet
[4] WGNHS, 2023, Wisconsin Ice-Margin Positions (Laurentide Ice Sheet) UPDATED
[5] Carlson, A., 2013, The Younger Dryas Climate Event. In: Elias, S.A. (editor). The Encyclopedia of Quaternary Science 3: 126–134. Amsterdam: Elsevier.
[6] The Bonneville Flood. Department of Geology and Geological Engineering. Colorado School of Mines. Retrieved 2023-12-21.
[7] Richards, M., Alvarez, W., at al., 2015, Triggering of the largest Deccan eruptions by the Chicxulub impact. Geological Society of America Bulletin, v 127, 1507–1520. doi:10.1130/B31167.1
[8] Hudson, H., 2021, Carrington Events, Annual Review of Astronomy and Astrophysics, v. 59, p. 1,445-477
[9] Chen, C. J., 2011, Physics of solar energy. Wiley, 370 pp. ISBN 978-0-470-64780-6
[10] Griggs, C.B., Lewis, C.M. and Kristovich, D.A., 2022. A late-glacial lake-effect climate regime and abundant tamarack in the Great Lakes Region, North America. Quaternary Research, 109, pp.83-101.
[11] Moore, A., Kennett, J. et al., 2023, Abu Hureyra, Syria, Part 2: Additional evidence supporting the catastrophic destruction of this prehistoric village by a cosmic airburst ~12,800 years ago. Airbursts and Cratering Impacts. 2023. Vol. 1(1). DOI: 10.14293/ACI.2023.0002
It seems that the scientists calculating sea level rise have a number of conflicting opinions. The original comment in the post was meant as support to the statement that an immediate 20 m sea level rise is highly unlikely, because of the corals, but also because an unrealistic amount of energy would be required, and that such a flood would cause massive onshore erosion that hasn't been observed. 5 m per decennium, century or millennium is still much less than 20 m in an instant. Thanks for sharing your insights.
Hi Betz12345, thanks for your interest. There are numerous articles describing coral reef growth rates during the last deglaciation. For example, https://www.nature.com/articles/s41467-017-00966-x, describe a growth rate of 5-6 m per millennium, and the sea-level rise curve commonly used https://dlab.epfl.ch/wikispeedia/wpcd/images/119/11900.png.htm is based on coral reef growth rates . All these coral reefs survived. To my knowledge no serious study proposed a sudden 20+ m sea level rise. Such a sudden, 20 m sea-level rise is therefore a hypothetical. If it had happened globally then most coral reef systems would have perished.